It is known to provide chairs, and wheelchairs in particular, having leg rests which are rotatable relative to a remainder of the chair, and which also extend and retract during rotation. For example, U.S. Pat. No. 5,259,664 (Cottle) discloses an extendable and retractable leg rest for a wheelchair having a rack and pinion assembly for extending and retracting the leg rest. A need exists for a powered extendible and retractable leg rest having a novel, simple, and robust mechanism to extend and retract the leg rest in accordance with rotation of the leg rest. A mechanism providing flexibility in the degree of extension and retraction achieved during rotation is thought to be particularly desirable.